Radiant energy signaling system



Aug. 20, 1957 u. s. BERGER ETAL RADIANT ENERGY SIGNALING SYSTEM 3Sheets-Sheet l Filed Aug. 14, 1953 TQQ u; s. BERGER- J F A/o/G ATTORNEYug 20, 1957 'u s. BERGER ET AL '2,803,744

RADIANT ENERGY SIGNALING SYSTEM 5 Sheets-Sheet 2 Filed Aug. l4, 1953VEA/robs; U S. BERGER ATTORNEY. y

3 Sheets-Sheet 3 /Nl/E/VTORS:

Aug. 20, 1957 U. s. BERGER ET AL RADIANT ENERGY SIGNALING SYSTEM FiledAug. 14, 1955 United States Patent O 2,803,744 RDIAN T ENERGY SIGNALINGSYSTEMA Application August 14, 1953, Serial No. 374,380 7 Claims; (Cl.Z50- 6) This invention relates to multi-channel radiant energy signalingsystems and, more particularly, to control equipment for use atcustomers stations in such systems.

When `a radiant energy signaling system is operated on a two-way basis,it has been the practice, especially in mobile radio-telephonecommunication systems, to employ onecarrier frequency for signalstransmitted from the central olii-ce to the customers stations and adilferent carrier frequency for signals sent from the customers stationsto the central oice. These two carrier frequency allocations constitutea single two-way radiant energy signaling channel which is used by thecustomers in much the same manner as a conventional telephone pa'rtyline. In' order to operate the customers transmitting` and receivingequipments over this two-frequency channel, each cstrle'rs station isusually provided with transmitting andV eceiving oscillators tunedrespectively to the transmitting and receiving carrier frequenciesallocated to the communication channel.

A single channel system of this type can be operated satisfactorilyprovided the number of customers stations is` not too large. However, ifthe number of customers stations is large, the quality of service can beimproved b'y employing two or more two-frequency radiant energysignaling channels for providing communication service on 'amultichannel basis. In the past, this has' been accomplished by dividingthe customers stations into groups, each group of stations beingassigned a dilferent `tvi/fofrequency channel for communicationpurposes, A1- though such a multi-channel system is an improvement overa single channel system, it has been determined that there are frequentinstances when a customer finds that his assigned ehannel'is b usy atthe time when he Wishes to place a call. Consequently, he is unable tomake his call immediately and is forced to monitor the channel until itbecomes idle.

Since the probability of all the channels being; busy simultaneously ata particular time is considerably less than the probability of anysingle channel being busy at that time, it can be understood that theoperating le'iciency ofthe system would be considerably improved bypermitting each customer to initiate calls over any one of thetwo-frequency channels that is idle. This may be accomplished byproviding each customers station with a plurality of pairs oftransmitting andreceiving osciilators, each pair being tuned foroperation over a respectively different one of the channels allocated tothe system, which can be selectively conditioned foroperation withth'etransmitting and receiving equipments at that station by manuallyoperable switching means. Thus, when a customer moves his manualselector switch from one channelselecting position to another, differentpairs of oscillators are alternatively enabled for operation with his`radio transmitter and receiver. With this method of operation, if acustomer attempts to initiate a call over one channel and nds that thechannel is busy, instead of vbeingforced to wait until the channelbecomes idle hecan immediately switch the operating frequencies of histransmitting and i ce receiving equipments to the two companionfrequencies allotted to another channel.

Although this method of operation facilitates the initiation of callsfrom the customers stations, it complicates the placing of calls fromthe central otnce to the customers stations. This is due to the factthat a. customer can receive` a call from the central oice only over theparticular channel to which his communication equipment happens to betuned at that time and an operator at the central olce has no way ofknowing the identity of this channel because the customer may haveplaced his selector switch in any one of its several channel-selectingpositions. Under these circumstances, it would be necessary for anoperator at the central oilice to attempt to communicate with a customerover rst one channel and then another. It can be understood thatsuch aprocedure would consume an appreciable amount of the operators time andwould also involve use of several diiferent channels thereby making themunnecessarily busy.

The placing of calls from the central oli-ice to the customers stationsmay be considerably simplified if the transmission of selective callingsignals from the central office to a customers station is restricted toonly a particular one of the signaling channels allotted to thecommunication system. In the past, this has been done by reserving oneof the channels allocated to a system as a calling channel andV by usingit solely for the transmission of selective calling signals. However,with the present increased use of the frequency spectrum, channel`allocations are too valuable to be used simply for selective callingpurposes. This can be avoided by allow ing each customer to callthecentral oflice over any channel he desires and by assigningeach group ofcustomers stations a respectively diiferent one of the channels for thetransmission of selective calling signals from the central of'ce, allchannels being free to be used for the transmission of regular messagesignals.

In accordance with this method, after each customer has used hisradio-telephone communication equipment, he should make certain that hischannel-selecting switch is left in the position for tuning hisequipment to the channel assigned to him for receiving selective callingsignals. If he neglects to `do this, then his equipment may be lefttuned to another channel in which event he will be unable to receiveselective calling signals as long as this condition exists. This is, ofcourse, quite undesir able and it would therefore be advantageous toprovide each customers station with means for automatically tun in g itsradio-telephone communication equipment, when idle, to the particularchannel assigned to it for the transmission of selective calling signalsfrom the central office.

Accordingly, it isan object of this invention to pro. vide a customersstation in a two-way multi-channel radiant energy signaling system withreverting means for automatically conditioning its signaling equipmentfor operation over a particular assigned signalingV channel whenever theequipment is in an idle condition.

It is also an object of this invention to provide a customers station ina system of the type mentioned above with locking means for preventingthe customers signaling equipment from being` conditioned for operationwith a signaling channel other than an assigned channel during periodswhen the assigned channel is idle.

These and other objects of the invention are accom plished by means thatare explained in detail hereinafter in connection with the followingdescription of the draw-` ing in' which:

Fig. l is a block diagram of a two-way multi-channel radiotelephonecommunication system comprising a central oliice and a plurality ofcustomers stations.

Fig. 2 is a circuit diagram of a customers radio-telephone signalingstation having incorporated therein one embodiment of the invention; and

Fig. 3 is a circuit diagram of another customers radiotelephonesignaling station employing a modication of the invention.

In Fig. l a two-way multi-channel radio telephone system is shown toinclude a radio telephone central oilice CO and a plurality of customersradio-telephone stations CSA, CSB, and CSZ. The system is furtherrepresented as having been allotted three two-frequency radiant cnergysignaling channels constituted by the frequency allocations FTA, FRA,FTB, PRB, FTZ and FRZ. The central office CO is shown to be providedwith three pairs of radio transmitters and radio receivers TA, RA, TB,RB, TZ, and RZ, each pair being tuned to a respectively different one ofthe signaling channels as is indicated inthe drawing. it is to beunderstood `that the system is not limited to the use of three signalingchannels but may employ any desired number. lf more channels are used,then the central office should bc provided with a correspondingly largernumber of pairs of radio transmitters and receivers as is indicated bythe broken lines BL. lt is to be further understood that, for purposesof simplicity, only three customers stations have been shown whereas thesystem actually includes a much larger number of such stations which, aswas stated above, are divided into groups. With this understanding inmind, it may be assumed that the three customers stations shown in Fig.l are representative of three different groups of of customers stationswith the group represented by station CSA being assigned the frequencyFTA for the transmission of selective calling signals from the centraloflice CO, the group represented 4by station CSB being assigned thefrequency FTB for receiving selective calling signals, and the groupsymbolized by station CSZ being assigned the frequency FTZ for the samepurpose. In accordance with the discussion above, these threefrequencies may also be used for the transmission of regular messagesignals to any of the customers stations. Furthermore, any of thecustomers stations may communicate with any of the central oice radioreceivers RA, RB, and RZ over their respective receiving frequenciesFRA, FRB, and FRZ provided they are not being used at that time by someother station.

For example, if the customer at the station CSA attempts to place a callto the central office CO over the frequency FRA but finds that thisfrequency is being used by some other station, he may operate hischannelselector switch to use the frequency FRB if it is idle. At thetermination of the call, he should move his channelselector switch backso as to leave his equipment tuned to receive selective calling signalsover the frequency FTA assigned to his group. If he does not do this,then his equipment will be left tuned to receive the frequency FTB withthe result that he will be unable to receive selective calling signalsover his assigned frequency FTA. To prevent this unintended lock-out,each customers station is provided with reverting means forautomatically tuning its communication equipment to its assigned channelafter the termination of a call made over another channel. Thesereverting means are described hereinafter in connection with thefollowing discussion of the station equipment shown in Fig. 2.

Fig. 2 shows the station equipment at any one of the customers stations,such as the station CSA. This equipment comprises atransmitting-receiving antenna lll coupled through a filter 12 to aradio transmitter 13 and a radio receiver i4. As is indicated in thedrawing, the radio transmitter 13 is provided with a plurality ofcarrier oscillators ORA, ORB, and ORZ and the radio receiver t4 isequipped with a plurality of beating oscillators OTA, OTB, and OTZ.These oscillators may be of any suitable type known to those skilled inthe art and are vdesigned to produce 'electric wave energy ofrespectively ditferent frequencies. The values of the frequencies of theenergy generated by the carrier oscillators ORA, ORB, and ORZ correspondrespectively to the carrier frequencies FRA, PRB, and FRZ to which thecentral oliice radio receivers RA, RB, and RZ are respectively tuned.The values of the frequencies of the energy produced by the beatingoscillators OTA, OTB, and OTZ correspond respectively to the carrierfrequencies FTA, FTB, and FTZ transmitted by the central oice radiotransmitters TA, TB andTZ, plus or minus the value of thc intermediatefrequency energy that is desired to be produced by the beating processin the radio receiver 14.

At is indicated in Fig. 2, the cathode leads 15 and 16 of theoscillators ORA and OTA, respectively, arev connected to a junctionpoint 17. Similarly, the cathode leads t8 and 'i9 of the oscillators ORBand OTB are connected to the junction point 20, and the cathode leads 21and 22 of the oscillators ORZ and OTZ are connected to the junctionpoint 23. In order to enable selectively anyI desired pair of theoscillators, the iunction points 17, 20,'

and 23 are connected respectively to contacts A, B, and Z` associatedwith a manually operable channelselector switch 25. The switch 25 isconnected over a conductor 26 to the make contact of a revert relay 52.When the relay 52 is energized in a manner described hereinafter, itoperates its armature thereby connecting groundv 27 to the conductor 26.

Under this condition, when it is desired to enable a particularpair ofoscillators, such as the oscillators ORA' and OTA, the switch Z5 ismoved to engage their asso-j ciatedswitch contact, which in thisinstance is the contact A, thereby connecting ground 27 to the leads 15and 16. This conditions the station equipment for communication over thechannel constituted by the two carrier frequency allocations FTA andFRA. The stationequipment can be conditioned for signaling over anyofthe other channels allotted to the system by moving thechannel-selector switch 25 to the appropriate contact. It is to beunderstood that the invention is not limited to this specific enablingmeans as any other suitable oscillator-l enabling means known to thoseskilled in the art may be used if desired. y The radio receiver 14 iscoupled over a conductor 31 to selective signal receiving equipment 32which may be of the type described in an article entitled Selectivecalling for mobile telephone service, written by B. P. Cottrell andpublished on pages 32 and 34, inclusive, of FM and Television, issue ofJanuary, 1948. As is explained in this article, the selector set 32 isprovided with a stepping switch 33 responsive to a [coded group ofimpulses. The selector set 32 also includes a call relay 35 which hasits energizing winding connected over its associated normally closedcontact 36 to the stepping switch contact 34. When contact 34 is engagedby the switch 33, a path is closed for current from battery 37 toenergize the call relay 35. f Since, in each group of customersstations, each customers stepping switch is responsive to a differentcoded group of impulses, the transmissionof a selective calling signalover the assigned calling channel will effect the energization of tihecall relay at only one of the customers stations, this station being theone to which that particular coded signal is assigned. When this occurs,the call relay at that station, such as the call relay 35, operates'itsarmatures. The operation of the left armature of relay 35 closes anobvious circuit over a lead 57 for current from battery 37 to energize acall lamp 38 and a lock-up relay 39 which is of the slow-to-releasetype. The operation of the right armature of relay 35 open-s the relaycontacts 36. However, the call relay 35 is maintained energized bycurrent from battery 37 which now travelsover the released armature of arestore relay 40 and over the operated armature of relay 35 to ground41. One side of the energizing winding of the restorerelay 40 is vconnected to the battery ,37 andthe otherY sidej isV connected by a lead42 to a contact 43 associated with a hook switch 44. The hook switch 44normally holds a telephone instrument 45 which is connected :by a lead.46 lto the radio `receiver 14 and by a lead 47 tothe radio transmitter13. Itis 4to be noted that the make .contact ofthe restore relay l40 isconnected by `a lead 48 Vto the junction point 49. One :side of thejunction point `49 is connected by a lead 5.0 to the right make .contactof the lock-up relay 39.. Another side of `the junction point .49 lisconnected `by a rlead `51 to one side of the energizing winding of arevert relay 5,2. Y

The ,revert :relay 52 is provided with ,an ,armature for connectingground 27 over its hack contact to the leads extending to the 4cathodesof the particular transmitting and `:receiving oscillators associated`with the calling channel @assigned to this Astation for the receptionof selective calling signals `.transmitted from the central oce CO. Inthis embodiment of the invention, it is assumed that the calling channelassigned to the station of Fig. `2 'is `the channel :constituted by thelfrequency allocations FTZ `and Accordingly, `the back `contact of therevert relay 52 is `shown to be connected over a conductor 53 to thejunction point 5,6 .of the `cathode leads 2 1 and `22 of the oscillatorsORZ and -GTZ associated `with this channel. It .is yto be `understoodthat -the conductor `53 :would Abe connected tothe `cathode leads of `adifferent pair of oscillaters if it ,should `be desired to assign adifferent channel as a calling channel.

Thus, during the stations idle `condition when the .teile- .phone.instrumentAS is fbeing held by the holder constimuted :by the hookswitch 44, the armature of ,the revert relay 52 is in its releasedposition so that `grou-nd 27 lis connected .over conductor 53 to theleads 21 and 22 of the oscillators QRZ and OTZ. This `automaticallycondi- :tions ,the station equipment for the reception of selectivecalling signals 'transmitted `from the central office `CO over theassigned vcalli-ng channel, even though the channelselecting switch 25has been left ina dierent channelselecting posi-tion.

,As -wasrstated above, each customer can initiate `a call to the.central office CO over any .one `ofthe channels that -is`idle.`Assuming that the customer at the station shown `at Fig. 2 `should wishtoplace va call, then he `would rst `remove his `telephone instrument`45 from its 'holder constituted by `the hook switch Y44. This connectsground 54 over the hook switch :contact 43 and lead 42 to `the wind-`ingof the restore relay 40 thereby `completing its energizing circuitrandcausing it tooperate its armature. "The .operation `of -thetarmatureof the restore relay 140 closes a lpath extending from the battery 37over -the operated .armature of relay 40, along conductor 48 to `thejunction `point `49., thenalong lconductor 51 through `,the winding Lofthe revert relay 52, `and `then over the back A,contactand .releasedleft .armature of the lock-up relay 39 to ground 455. -This `causesV.the relay 52 .to operate .its armature thereby .disconnecting ground27 `from the `lead 53 ,and `connectingit to the lead 26, thus activating,the channel- ,selector switch 25.

If .the .switch 25 .is left in the position to engage its contact A,.as-is shown in Fig. 2, :the oscllatorsfORA and .OTA `will now beenabled and `thc station equipment will .beconditioned for`operationover their associated channel constituted by the frequencyallocations FTA and FRA ,provided this channel is idle. `Ifthis channelhappens to `be .busy tat .this time, which .can `be determined bylistening in.on Vthe .telephone 45, `then ther customer; should`rnovethe l,switch 25 ;to `a different channel-selecting position, such.as to the `:position :in which it will engage its contact B.'lhis-'enablesrthe oscillators OTB andORB and conditions .the `station`equipment -for operation over the channel constituted .by-the frequencyvallocations FTB and FRB. rlffthis ,channel.is idle, the customer -thenproceeds with his rcall.

At lthefterminationofthe call, the customer places the telephone 45 onits "hook `switch `holder Y44. :It would `alsoflnefappropriate.for him`to move his `channel-.se1ector switch 25 to engage its contact Z forconditioning the station equipment `for receiving selective calling`signals over the assigned calling lfrequency allocation FTZ. How.-ever, this is not `necessary because, rwhen thertelephone 45 is placedon the hook switch 44, Lthe hoo-k switch 4 4 dis*- engages its contact43 thereby opening the circuit `described above `for .energizing Atherevert relay 52. Accordingly, relay `52 now releases its armaturethereby disconnecting ground 27 from the channel-selector switch 25which is, in effect, now disabled. At `this same time, fthe release ofthe `armature of relay 52 connects ground 27 to the junction point 56thereby enabling the oscillators OTZ and GRZ associated with theassigned calling lchannel. Thus, the station equipment is automaticallyrestored tothe condition for operation over the assigned calling channelregardless `of theposition in which the customer may have left his.channel-selector switch 25.

.In placing a. call from the central otlicewCO to any one of thecustomers stations, the central oce operator `transmits over therespectively assigned calling carrier frequency `the particularselective calling signal which is assignedto the desired customersstation. For example, in calling the customers station shown in Fig. 2,the appropriate selective calling signal is transmitted over the carrierfrequency FTZ and, when received, causes Ithe stepping switch 33 `in`the selective signal receiving equipment 32 to move into engagementwith its contact 34. As `was stated above, this closes a path forcurrent `*from .battery 37 :to energize the call relay 35 whichconsequently operates its armatures.

The relay contacts associa-ted with the right armature `of relay 35 are`of the `make-beforeibr`eak type so that .the operation .of thisarmature closes a locking circuit vfor relay 35 over the releasedarmature of relay 40 .before the contacts 36 are opened. At this sametime, the Yoperation of the left armature of relay 35 connects battery37 `to the call lamp 38 and to the energizing winding of the lockuprelay 39. This causes relay 39 to operate its armatures. `The rightarmature now connects the -winding of -relay 39 over conductors 50 and48 to the make contact of the restore relay 40. The operation of theleft armature `of'rclay 39 disconnects ground 55 .from `the winding of:the revertrelay 52 so that it cannotbe energized `until after relay 39`has been de-energized and has released its armatures. Thus, thearmature of lrelay `52 `is Vlocked in its released position where itconnect-s ground `27 to the junction `point 56 thereby maintaining theoscillators ORZ and O-TZ, which are associatedwith the assigned callingchannel, in an enabled condition.

Upon noticing :that his call lamp 38 is illuminated, the customer at thestation shown'in Fig. 2 answers the call by removing his telephone 45from lthe hook switch 44 nthus permitting the hook switch 44 to engageits "con- ,tact 43. This closes the circuit for energizing -the restorerelay 40 which operatesits armature to effect the de-ener- `gizatlon `ofthe call relay 35. The energization of the restore relay 40 also.effects Vthe resto-ration of the stepping switch 33 to its initialposition in the manner described in the above-mentioned article `by B.VP. Cottrell. lThe call relay 35 now releases `its armatures to`disconnect battery 3,7 ,from the .conductor 57 leadingto the call lamp38 and lto the winding of the lock-up `relay 39.

IHowever, at .this same time, the operation `of the arma- :ture of:relay 40 applies current-from battery 37 over conductors ,48 and 50 `to`the right make contact of lthe lockup relay 39. `Since relay 39 is ofthe slowto-release ltype, its `right :armature will 'be held against itsmake contact `long enough for-,its windingito .receive the current nowapplied over the operated armature of relay 40. Therefore,thexlockwup.relay 39 will remain energized and its armatures `willbe maintainedoperated. A portion of the current now applied `overtthe rightarmatureof `relay 39 is also supplied to illuminate the call lamp 38."This serves to inform the customer at that station thatuhischannebselector switch 25 is, in .elect disabled and that 'nel is idle.

from the hook switch 144.

his station equipment is locked in the condition foropera- -tion overthe assigned calling channel. i

' At the termination of this call, the customer hangs his telephone 45on the hook switch 44 thereby causing the hook switch 44 to disengageits contact 43. This opens the energizing circuit of the restore relay40 and causes it to release its armature. The release of the armature ofrelay 40 disconnects battery 37 from the right make contact of thelock-up relay 39. This causes relay 39 to release its armatures and alsoextinguishes the call lamp 38 to inform the customer that his stationequipment has been restored to its normal idle condition.

As was stated above, the customers station shown in Fig. 2 is soequipped as to enable the customer to place a call over any one of thechannels that is idle. Accordingly, the customer may place a call overone of the unassigned channels even though his assigned calling chan-This makes that particular unassigned channel become busy with theresult that the central oflice operator cannot use it at that time forthe transmission of selective calling signals to any of the customers inthe group to which that channel is assigned as a calling channel.Therefore, in order to equally distribute the load iamong the allottedsignaling channels and also to pre- -vent a customer from making one ofthe other channels `unnecessarily busy at a time when his assignedcalling channel is idle, it is desirable to provide the customers4stations with locking means for preventing the customers from placingcalls over other channels when their respecftively assigned callingrchannels are idle. These locking -means are described hereinafter inconnection with the following discussion of the station equipment shownin 'Fig 3.

1 The station equipment shown in Fig. 3 is basically the vsame as thatshown in Fig. 2 except that it is provided with additional equipmentwhich includes a codan control circuit 160 with an associated codanrelay 161, an

-extra armature and set of contacts for the restore relay 140, andadditional circuit conductors. The codan control circuit 160 may be ofany suitable type known to those skilled in the art, such as the typedescribed on page 653 of F. E. Termans Radio Engineers Handbook. ThisVis the type which responds to the reception of carrier energy having amagnitude in excess of a pre-selected threshold value by producing avoltage change or a current change at a point in its circuit which willefect the Yde-energization of the codan relay 161 for causing it torelease its armature. Conversely, it responds to an ab- -sence ofcarrier energy above the threshold value by effecting the energizationof the codan relay 161 for causing it to operate its armature.

This station equipment functions in the same manner as the stationequipment shown in Fig. 2 when a selective .calling signal is receivedfrom the central office operator and the customer answers by removinghis telephone 145 However, it functions difterently from the stationequipment of Fig. 2 when the cus- `temer initiates a call and this willnow be described.

In the idle condition of the station shown in Fig. 3, the call relay135, the restore relay 140, the lock-up relay 139, and the revert relay152 are all de-energized. Consequently, ground 127 is connected over thereleased left armature of the revert relay 152 to the junction point4156 avd then over the leads 121 and 122 to the oscillators -OTZ and ORZassociated with the calling channel .assigned to this station, ytherebyconditioning the station equipment for operation over this channelregardless of the position of the channel-selector switch 125. If thisvchannel is idle, then the codan control circuit 160 will 'cause thecodan relay 161 to become energized as was stated above. Accordingly,the armature of the codan Vrelay 161 will now be in its operatedposition for connecting ground 162 over the lead 163 to the right makecontact of the restore relay 140.

Now, when the customer at the station shown in Fig. 3

wishes to place a call, he first removes his telephone 145 from the hookswitch 144. This connects ground 154 over the hook switch contact 143and the lead 142 to the winding of the restore relay 140, therebycompleting its energizing circuit and causing it to operate itsarmatures. The operation of the right armature of relay 140 closes acircuit extending from ground 162 over the operated armature of thecodan relay 161, along conductor 163, over the operated right armatureof relay 140, along conductor 164 to the junction point 165, and thenalong conductor 166 to the winding of the codan relay 161. Consequently,the codan relay 161 will now, in effect, be locked up under the controlof the restore relay 140 and the hook switch 144 and will hold itsarmature in its operated position regardless of any voltage or currentchanges that may subsequently occur in the codan control circuit 160.

At this time, the operation of the left armature of relay 140 connectsbattery 137 over conductor 148 to the junction point 149 and then overthe lead 151 to the winding of the revert relay 152. However, eventhough the left armature of relay 139 is in its released position, theenergizing circuit of the revert relay 152 is open at the back contactof the codan relay 161 so that relay 152 will be held in its unenergizedcondition to prevent ground 127 from being applied over conductor 126 tothe channelselector switch 125. Thus, any operation of thechannelselector switch at this time will be ineffectual to condition thestation equipment for operation over any channel other than the assignedcalling channel.

As soon as the customer proceeds with his call, this channel becomesbusy with the result that a voltage or current change is produced in thecodan control circuit 160. This change cannot now effect thede-energization of the codan relay 161 because, as was explained above,it is locked in its energized condition under the control of the hookswitch 144. The station equipment therefore remains locked in thecondition for operation over the assigned calling channel for theduration of the call.

At the termination of the call, the customer replaces his telephone 145on the hook switch 144 thereby disengaging it from its contact 143. Thisde-energizes the restore relay which releases its armatures to restorethe station equipment to its normal idle condition.

If, at the time when the customer at the station shown in Fig. 3 liftedup his telephone 145 to initiate a call, the assigned calling channelshould be busy, then, as was explained above, the codan relay 161 wouldbe deenergized and its armature would be in its released position forconnecting ground 162 over the released left armature of relay 139 toone side of the Winding of the revert relay 152. Under this condition,when relay 140 operates its armatures in response to the engagement ofthe hook switch 144 with its contact 143, the left armature of relay 140will connect battery 137 over leads 148 and 151 to the other side of thewinding of relay 152. This causes relay 152 to operate its armatures.The left armature of relay 152 now connects ground 127 over lead 126 toenable the channel-selector switch 125 so that the station equipment maynow be conditioned for operation over any one of the channels that isidle.

At the same time, the operation of the right armature of the revertrelay 152 connects ground 167 to the junction point 168 thereby shuntingthe codan relay 161 and, in effect, locking it in its unenergizedcondition for the duration of the call. If the codan relay 161 were ynotthus held de-energized, then it might subsequently be energized inresponse to a momentary fading in the strength of the received carrier.In such an event, the operation of the armature of the codan relay 161would open the energizing circuit of the revert relay 152 which, inturn, would release its armatures to disconnect ground 127 from thechannel-selector switch 125 thereby disabling the selected oscillators.However, this'is prevented by locking the codan relay 161 in itsunenergized condition with the result that the station equipment remainsconditioned for operation over the selected channel for the duration ofthe call.

This particular embodiment of the invention has been described in orderto explain the principles and features of operation of the invention. Itis to be understood that the invention is not limited to the specificcircuit construction shown in the drawing as various modifications maybe made Without exceeding the scope of the invention which is to belimited only by the claims appended hereto.

What is claimed is:

1. In a radiant energy communication system having a plurality ofradiant energy signaling channels allotted thereto for the transmissionof carrier waves, a signaling station comprising in combination carrierWave signaling equipment, first means for effecting the placing of saidequipment in condition for operation over any one of said channels,second means for effecting the placing of said equipment in conditionfor operation over only an assigned one of said channels, a firstelectroresponsive device for enabling said first and second meansalternatively, a rst circuit for energizing said device, said firstcircuit having first and second portions connected in series, said firstportion being normally open, said second portion being normally closed,a telephone instrument coupled to said signaling equipment, a holder forremovably holding said instrument, and a second electroresponsive deviceresponsive to the removal of said instrument from said holder forclosing said first portion of said first circuit, said signaling stationbeing additionally characterized by the fact that it further comprisesselective signal receiving equipment for responding to selective callingsignals received at said station, said selective signal receivingequipment including a normally unenergized call relay, a thirdelectroresponsive device, and a second circuit for energizing said thirdelectroresponsive device, said second circuit being normally open, saidselective signal receiving equipment being responsive to the receptionof an assigned selective calling signal for energizing said call relay,means actuated in response to the energization of said call relay forclosing said second circuit, said third electroresponsive device beingresponsive to the closure of said second circuit for opening said secondportion of said first circuit.

2. A radiant energy communication system in accordance With claim lwherein said signaling station includes a locking circuit for holdingsaid third electro-responsive device energized after closure of saidsecond circuit, said locking circuit being normally open, said holderbeing responsive to the removal of said instrument therefrom foreffecting the opening of said second circuit after its closure and foreffecting the closure of said locking circuit.

3. In a radiant energy communication system having a plurality ofradiant energy signaling channels allotted thereto for the transmissionof carrier Waves, a signaling station comprising in combination carrierWave signaling equipment, first means for effecting the placing of saidequipment in the condition for operation over any one of said channels,second means for effecting the placing of said equipment in thecondition for operation over only an assigned one of said channels, afirst electroresponsive device for enabling said first and second meansalternatively, a circuit for energizing said device, said circuit havingfirst and second portions in series, a telephone instrument coupled tosaid signaling equipment, a holder for removably holding saidinstrument, a second electroresponsive device responsive to the removalof said instrument from said holder for closing said first portion ofsaid circuit, and a carrier-responsive device responsive to thereception of carrier waves at said station for closing a second portionof said circuit, said carrier-responsive device being responsive to theabsence of received carrier waves at said station for holding saidsecond portion of said circuit open.

4. In a radiant energy communication system having a plurality ofradiant energy signaling channels allotted thereto for the transmissionof carrier waves, a signaling station comprising in combination carrierwave signaling equipment, rst means for effecting the conditioning ofsaid equipment for operation over any one of said channels, second meansfor effecting the conditioning of said equipment for operation over onlyan assigned one of said channels, a first electroresponsive device forenabling said first and Second means alternatively, a control relayhaving an energized condition and a de-energized condition,carrier-responsive means responsive to the reception of carrier Waves atsaid station for placing said relay in one of said conditions, saidcarrier-responsive means being responsive to an absence of receivedcarrier waves at said station for placing said relay in the other of itsconditions, a circuit for energizing said device, said circuit havingfirst and second portions in series, said first portion being heldclosed when said relay is in one condition and being held open when saidrelay is in its other condition, said second portion being normallyopen, a telephone instrument coupled to said signaling equipment, aholder for removably holding said instrlument, and a secondelectroresponsive device responsive to the removal of said instrumentfrom said holder for closing said second portion of said circuit.

5. A radiant energy communication system in accordance with claim 4wherein said signaling station includes a `shunt circuit for shuntingsaid control relay, said shunt circuit being normally open, and aninstrumentality actuated by said first electroresponsive device forclosing said shunt circuit.

6. A radiant energy communication system in accordance with claim 4wherein said signaling station includes a locking circuit for holdingsaid control relay in its energized condition, said locking circuitbeing normally open, and an instrumentality actuated by said secondelectro responsive device for closing said locking circuit.

7. A radiant energy communication system in accordance with claim 4wherein said signaling station includes a locking circuit for saidcontrol relay, said locking circuit having a closed condition forholding said relay in its energized condition, said locking circuit alsohaving an open condition, and an instrumentality actuated by said relayfor placing said locking circuit in its open condition.

References Cited-in the file of this patent UNITED STATES PATENTS2,330,241 Roberts Sept. 28, 1943 2,429,607 Capen Oct. 28, 1947 2,479,701Ress Aug. 23, 1949 2,649,541 McDavitt Aug. 18, 1953 2,670,435 MitchellFeb. 23, 1954 2,694,141 Mitchell Nov. 9, 1954

